The present invention relates to electrical receptacles having ground fault circuit interruption capability, hereinafter termed GFI receptacles; and more specifically, the invention relates to novel constructions and arrangements of circuitry components of such receptacles.
In addition to the usual load terminals, mounting strap, body and housing portions etc. of standard wall receptacles, GFI receptacles include means for sensing an imbalance in current flow through the hot and neutral conductors, circuit means responsive to such imbalance for generating a "trip" signal, and a set of contacts movable to open the circuit in response to the trip signal. A wound toroidal core through which the condcutors pass to provide current-sensing transformers is commonly used as the sensing means, and a solenoid including a coil and movable armature, together with appropriate mechanical couplings and biasing means, functions as the contact-opening means. In addition, GFI receptacles must include means for intentionally introducing a trip signal to permit periodic testing of the device, and means for resetting the contacts in their original position after tripping. It is also desirable that the circuit means include protective means for preventing damage to circuit components due to the presence of momentary high voltage spikes caused by lightning strikes, or other transient conditions.
Although GFI receptacles require a great deal many more components, both electrical and mechanical, than ordinary wall receptacles, it is desirable that the overall size of the two be essentially the same in order to permit mounting in the same, standard junction boxes. This requirement has led to the development of various improvements in the design and construction of GFI receptacles, including miniaturization of circuit components and the layout thereof, the use of certain components, both mechanical and electrical, to perform multiple functions, etc. In some cases, however, reductions in the size and number of components to fit in a given space and still provide a variety of desired functions has resulted in greater complexity and cost of fabrication of GFI receptacles.
It is a principal object of the present invention to provide a GFI receptacle having electrical and mechanical components of GFI cicuitry which permit compact and economical construction and, at the same time, provide ease of fabrication and assembly.
A more specific object is to provide a circuit design for incorporation in a GFI receptacle which includes means for protecting circuit components from damage due to circuit transients, yet eliminates the elements commonly used to provide this function.
A further object is to provide GFI receptacle circuitry having novel and improved means for testing proper operation of the device.
Another object is to provide a GFI receptacle having a circuit board with all components surface mounted in a compact format.
A still further object is to provide a GFI receptacle having novel and improved means for mounting the ground fault sensing and grounded neutral coils, as well as the solenoid coil, on the circuit board which carries the GFI circuit components.
Other objects will in part be obvious and will in part appear hereinafter.